Bleaching paper pulp



' or acid. ll

results in the li remaining bleach which attacks the color,

Patented Sept. 25, 1923.

UNITED STATES JOHN C. BAKER, OF NUTLEY, NEW JERSEY.

BLEACKING PAPER PULP.

1T0 Drawing.

To all whom it may concern:

Be it known that I, JOHN C, BAKER, a citizen' of the United States of America,

. residing at Nutley, Essex County, State of New Jersey, have invented certain new and useful Improvements in Bleaching, Paper Pulp, of which the following is a full, clear, and exact description.

The process of bleaching paper pulp has heretofore been carried out almost universally by the use of a suflicient amount of a solution of bleaching powder which is added to the unbleached pulp. Under ordinary conditions the bleaching action is continued until its completion, which requires from three to six hours, but at or before the expiration of this period it is customary to add an acid to improve the final bleaching cfi'ect. This addition of acid, howeyer, is usually inefi'ective in producing the desired result, and, in fact, is frequently disadvantageous by increasing instead of diminishing the color of the pulp and thus actually impairing, rather than improving, the intended bleaching action.

By a, protracted course of experiment and investigation I have ascertained the reason for the unsatisfactory colors in such product as wood ulp, and have discovered a new method En very greatly increasing the whiteness of the finished stock without in any way impairing its properties, and this application for Letters Patent is based upon that discovery, which I shall now describe in detail.

I have found that there may exist two differently actin colorin matters which are left in the near y bleac ed pulp. One of these is the principal color1 n matter of the pulp which remains as ,t e result of incomplete bleachin but which is capable of bei'n eliminated %y the continued bleaching action, and the other is a color which cannot be eliminated by further bleaching no ;i entirely by the usual step of adding an em When this first-named or unbleached color remainsv in the ulp the addition of acid tion of chlorine from and forms fixed yellows which cannot be then removed, and this is the main cause of the addition of the retrogression followin On the other hand the other coloring matter present in the pulp is not aifected by the use of acid asordinarily practiced Application filed January 7, 1922. Serial Ro. 527,728.

for reasons which will be explained, although, if a great excess of acid is added, or i the pulp be washed and then acidi fied, or if acid be added andthe pulp be allowed to stand for a long period, as, for example, over night, then the pulp becomes very white.

These methods are not, however, practicable nor feasible because of the impairment by their use of the fibre strength, or because of the increase of time involved or the expense and complication of the lwashing equipment required for the proper removal of the acid. 7

I have found that the color may be eliminated and color retrogression effectively prevented if the residual availablechlorine, which remains at the point of complete bleaching action is destroyed by a reducing agent, and the acid then either simultaneously or subsequently added.

The reasons for these steps will be understood from the following:

CaOCl, aciddHOCl calcium salt,

in which CaOCl is calcium hypochloritc, and HOCl is hypochlorous acid. The hypochlorous acid formed is a very Weak acid and is not ufiiciently ionized to yield hydrogen ions which are coloring matter in the pulp. The addition of acid is, therefore, without sensible effect.

The addition of stronger acid beyond that capable of changing the tively smallamount of acid is all suflicient to produce the desired result.

The addition of more reducing agent beyond that required to destroy the hypochlorite, produces a further whitening effect on the pulp in the presence of the added acid.-

In the carrying out of my new process, there are many agents which can be used such as hyposulphate of sulphites with sulphuric acid or oxalic acid alone, but for economy of operation and for obtaining the most satisfactory results, the most desirable agent is 5111 bur dio g'de, asthis re ucing an as an acidifying agent, and

operates both as a may be used in amounts in excess of that required for destroying the hypochlorite without damage or injury, and will further improve the color. Other acids may be used with the sulphur dioxide, if sufiicient be not employed for the complete destruction of the hypochlorite, to produce the desired results.

The reactions occurring in the process may be thus expressed:

(39001, so, H O CaCl u son,

or in other words, calcium hypochlorite plus sulphur dioxide plus water gives calcium chloride plus sulphuric acid.

This removes the oxidizing potential and adds acid at the same time. A. further reaction can occur with the color when more S0 is added which results in additional color removal.

I have herein described the application of the process, the ordinary and well known bleaching process, but its use is not limited in this respect. For example, I may use it in conjunction with a process of my invention which I have set forth in an application Serial No. 485,701, filed July 18, 1921.

Having now described my invention, what I claim is:

1. The process of bleaching pulp by an agent containing chlorine herein described, which consists in continuing the process until the bleaching effect is practically complete, then neutralizing or destroying in the pulp the remaining chlorine component and acidifying the pulp.

2. The process of bleaching pulp herein described which consists in exposing the pulp to the action of a bleaching agent containing chlorine until the bleaching efi'cct is practically complete, then adding an agent to destroy the remaining chlorine and then adding an acid.

3. The process of bleaching pulp herein described which consists in exposing the pulp to the action of a bleaching agent containing. chlorine until the bleaching effect is practically complete, and then adding sulphur dioxide. L

In testimony'whereof I hereto afiix my signature.

JOHN C. BAKER.

CERTIFICATE OF CORRECTION.

Patent No. 1,1;6B,695. September 2 1923.

JOHN C. BAKER. I It is hereby certified that error appears in'the printed epeci-fication 9f the above numbered patent requiring correction as follows: Page 1, aec- 0nd column, line 107, for the word "of" read,--or--; and mm: the said Letter: Patent should be read with thia correction therein that the same may center]: to the record or the case in the Patent Office.

Signed and sealed this 50th day of July, A. D. 19140.

Henry Van Aradale J (Seal) Acting Commissioner of Patents 

